The research proposed in this application deals with problems of the genetic control of growth and differentiation in mammals. For this purpose mutations in the mouse with effects on development and differentiation serve as tools of investigation. Our proposal includes the following topics: 1. Identification of individual mutations affecting growth and differentiation and genetic analysis of their mode of transmission. 2. Elucidation of mechanisms of gene action and of genetic control of growth and differentiation. 3. Studies of the genetic control and correlation of biochemical differentiation and morphogenesis. 4. The dissection of the fine structure of complex genetic loci controlling differentiation. These investigations are relevant to the problem of congenital abnormalities and inborn errors of metabolism in man. Mutations in the mouse serve as model systems for similar conditions in man.